In recent years, an electron tube having a photocathode and an electron-bombarded semiconductor device has been proposed. The photocathode emits a photoelectron in response to an incident light. The electron-bombarded semiconductor device multiplies and detects a photoelectron. As the electron-bombarded semiconductor device, an avalanche photodiode (hereinafter, referred to as APD) has been mainly used.
In an electron tube using the APD, an entrance window and a conductive stem are disposed opposite to each other at both ends of an insulating container. The photocathode is formed on the internal surface of the entrance window, and the APD is disposed on the conductive stem. A ground voltage is applied to the conductive stem, and a negative high voltage is applied to the photocathode. The conductive stem is electrically insulated from the photocathode by the insulating container. Therefore, the vicinity of the photocathode of the insulating container becomes a negative high voltage (refer to, for example, Patent Document 1 or 2).
Further, as the electron tube using the APD, an electron tube in which a conductive stem protrudes inside the insulating container has been proposed (refer to, for example, Patent Document 3)
[Patent Document 1]
Japanese Patent Application Laid-Open Publication No. 8-148113 (pages 3 to 8, FIG. 1)
[Patent Document 2]
Japanese Patent Application Laid-Open Publication No. 9-312145 (pages 3 to 6, FIG. 1)
[Patent Document 3]
Japanese Patent Application Laid-Open Publication No. 9-297055 (pages 4 to 9, FIG. 4)